Search results for "Passive transport"
showing 10 items of 12 documents
Importance of meteorological variables for aeroplankton dispersal in an urban environment
2016
Passive wind dispersal is one of the major mechanisms through which organisms disperse and colonize new areas. The detailed comprehension of which factors affect this process may help to preserve its efficiency for years to come. This is especially important in the current context of climate change, which may seriously alter weather regimes that drive dispersal, and is crucial in urban contexts, where biodiversity is dramatically threatened by pollution and fragmentation of natural patches. Despite its interest, the analysis of factors affecting aeroplankton dispersal in urban environments is rare in literature. We sampled aeroplankton community uninterruptedly every 4 hours from 17th May t…
Kinetic modelling of passive transport and active efflux of a fluoroquinolone across Caco-2 cells using a compartmental approach in NONMEM.
2005
The purpose was to develop a general mathematical model for estimating passive permeability and efflux transport parameters from in vitro cell culture experiments. The procedure is applicable for linear and non-linear transport of drug with time,10 or10% of drug transport, negligible or relevant back flow, and would allow the adequate correction in the case of relevant mass balance problems. A compartmental kinetic approach was used and the transport barriers were described quantitatively in terms of apical and basolateral clearances. The method can be applied when sink conditions are not achieved and it allows the evaluation of the location of the transporter and its binding site. In this …
Development of predictive retention-activity relationship models of non-steroidal anti-inflammatory drugs by micellar liquid chromatography: comparis…
2000
The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that under adequate experimental conditions the solute partitioning into chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis for drug and metabolite uptake, passive transport across membranes and bioaccumulation. The use of micellar solutions of Brij35 as mobile phases in reversed-phase liquid chromatography has proven to be valid to predict some biological activities of different kinds of drugs. In this study, quantitative retention-activity relationship (QRAR) models to describe som…
Effects of pH on ion transport in weak amphoteric membranes
1997
Abstract We have studied theoretically the effect of pH on the ion transport through amphoteric polymer membranes composed of weak polyelectrolytes where the charged groups are randomly distributed along the axial direction of the membrane. This system serves as a simplified model for the pH controlled ion transport and drug delivery through membranes of biological interest. The theoretical approach employed is based on the Nernst-Planck equations. The complete system of electrical charges formed by: (i) the pH dependent, amphoretic membrane fixed charge, and (ii) the four mobile charges (the salt ions and the hydrogen and hydroxide ions) have been taken into account without any additional …
pH and supporting electrolyte concentration effects on the passive transport of cationic and anionic drugs through fixed charge membranes
1999
Abstract The effects of pH and supporting electrolyte concentration on the passive transport of an ionized (cationic or anionic) drug through a thick fixed charge membrane have been theoretically studied. This system constitutes a simplified model for the pH controlled ion transport and drug delivery through membranes of biological and pharmaceutical interest. Calculations were carried out for different values of the membrane fixed charge, supporting electrolyte and drug concentrations covering a broad range of the conditions usually found in experiments. The theoretical approach employed is based on the Nernst–Planck flux equations, and all of the species present in the system (the neutral…
Passive Transport of Ionic Drugs through Membranes with pH-Dependent Fixed Charges
2001
We have studied both theoretically and experimentally the passive transport of ionic drugs through membranes with pH-dependent fixed charge. The system considered constitutes a simplified model for pH-controlled drug delivery through membranes of biochemical and pharmaceutical interest. The theoretical approach employed is based on the Nernst-Planck flux equations and all of the species present in the system (the neutral or ionic drug and the hydrogen and hydroxide ions) have been taken into account together with a Langmuir-type isotherm for the adsorption of the ionic drug onto the membrane surface. The membrane permeabilities of cationic, anionic, and neutral drugs through porous membrane…
Retention-activity relationship studies of benzodiazepines by micellar liquid chromatography
1999
Solute partitioning into lipid bilayers of biological membranes is the basis for drug and metabolite uptake, passive transport across membranes and bioaccumulation. In order to emulate in vitro the partitioning process in the biomembranes, different approaches have been proposed. The use of micellar solutions as mobile phases in reversed-phase liquid chromatography (micellar liquid chromatography, MLC) has proven to be valid in the prediction of the biological activities of local anesthetics, catecholamines and barbiturates. In this paper we focus our attention on benzodiazepines. The retention of benzodiazepines using different concentrations of Brij35 as micellar mobile phase in modified …
Development of predictive retention-activity relationship models of antipsychotic drugs by micellar liquid chromatography
1999
The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that in adequate experimental conditions the solute partitioning into the chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis of drug and metabolite uptake, passive transport across membranes and bioaocumulation. The use of micellar solutions of Brij35 as mobile phases in reversed liquid chromatography has proven to be valid in predicting some biological activities of different kinds of drugs. In this paper, the correlations between the logarithm of capacity factors and pharmacokineti…
Development of predictive retention-activity models of butyrophenones by biopartitioning micellar chromatography
2001
The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that in adequate experimental conditions the solute partitioning into the chromatographic system can emulate the solute partitioning into lipid bilayers of biological membranes, which is the basis of drug and metabolite uptake, passive transport across membranes and bioaccumulation. The use of retention data obtained in biopartitioning micellar chromatography (BMC) has been demonstrated to be helpful in describing the biological behaviour of different kinds of drugs. In this chromatographic system, polioxyethylene 23 lauryl ether Brij35 micellar mobile p…
Development of Predictive Retention-Activity Relationship Models of Barbiturates by Micellar Liquid Chromatography
2000
The need to get a tool for biological parameters estimation of new compounds for clinical applications, supports the postulation of predictive models as an alternative to conventional classical assays being no necessary the use of experimentation in animals. Our main aim in this work is to determine correlations between the logarithm of capacity factors and preclinical pharmacology and therapeutic efficacy parameters of barbiturates. The predictive and interpretative capability of quantitative chromatographic retention-biological activity models is supported by the fact that in adequate experimental conditions the solute partitioning into chromatographic system can emulate the solute partit…